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ETCS Baseline 4 – what is new? - exclusively for New In Signal by Francesca Leoci

Francesca Leoci, from MERMEC S.p.A, Italy
Francesca, thank you for joining us today.
As an expert in the ERTMS/ETCS system,
we're excited to learn from your insights.
Let's jump right into it.
Latest News | Francesca Leoci
ETCS Baseline 4 – what is new?
In July 2024, Baseline 4 R1 of the CCS TSI was released, with the introduction of Baseline 0 for the FRMCS and Baseline 1 for ATO.
The link to the complete documentation relative to this new baseline is the following:
• CCS TSI Mandatory Specifications ETCS B4 R1 RMR:GSM-R B1 MR1 FRMCS B0 ATO B1
The new Baseline introduces important innovations, especially for the definition of the following new technologies:
• Future Railway Mobile Communication System (FRMCS);
• Automatic Train Operation (ATO).
Before describing these new technologies, let’s start by highlighting some important differences compared to Baseline 3 R2.
From an application point of view, Level 3 has been removed, delegating any Train Integrity supervision functionality to Level 2.
The image below indicates how the new Level 2 of the Baseline 4 R1 has been implemented.
BASELINE 3 R2


BASELINE 4 R1

In Baseline 4 R1 the Train Integrity (or Train Separation) and Train Detection functions in Level 2:
• can be performed by the trackside equipment of the underlying signaling system (similarly to Baseline 3 R2);
• can be performed by the RBC together with the On-Board Subsystem (sending the Position Report with the information relating to Train Integrity).
Another functional innovation is the introduction of the “Supervised Manoeuvre (SM)” operating mode.
The “Supervised Manoeuvre” allows enhanced supervision of shunting movements, similar to the Full Supervision operating mode, when the cab is not necessarily at the front of the shunting cab.
Executing a procedure initiated by the driver described in Subset 26-05 is the only way to transition to SM mode.
The document “ETCS Driver Machine Interface” (ERA_ERTMS_015560) introduces functional requirements for the “Supervised Manoeuvre” operating mode, including the icon to be displayed on DMI () with its viewing position.

One last functional innovation introduced in Baseline 4 R1 that needs to be indicated is the management of odometer accuracy.
The Onboard Subsystem monitors the odometer’s accuracy based on the separate accumulation of underestimation and overestimation when measuring the train’s movement over a fixed distance.
In Baseline 4 R1 the On-Board Subsystem shall classify the odometer performance as impaired when certain conditions defined by the new functional requirements are verified.
For this purpose, the following new fixed parameters have been introduced:
• Total distance of accumulated movements: distance value in which the Onboard Subsystem shall store the accumulated underestimation/overestimation in measuring the train movements.
• Maximum distance interval: fixed interval in which the check of the odometer accuracy shall be performed periodically.
• Impairment threshold: The threshold value to be used when the Onboard Subsystem analyses the odometer performance and considers it impaired.
• Safety threshold: When any of the accumulated underestimation/overestimation in measuring the movements over the defined total distance travelled exceeds the safety threshold, the ERTMS/ETCS Onboard equipment switches to System Failure Operating Mode.
For the management of the tolerance of Big Metal Masses, additional functional requirements have been introduced to indicate when the Onboard Subsystem must ignore alarms generated by the BTM and its reaction when an alarm is not ignored.
As indicated at the beginning of the article, two important innovations introduced in Baseline 4 R1 are FRMCS and ATO.
The FRMCS acronym, which stands for Future Railway Mobile Communication System, was introduced to provide a successor to GSM-R and cope with its predicted obsolescence.
The study and definition of this new communication system are in course, but we can say that the FRMCS will be applicable for operational purposes covering urban and Metro Rail and will provide communication services applicable for operational purposes covering high-speed and Conventional Rail Systems.
The following figure (source AT-7800) indicates the FRMCS layered architecture.

Since this new communication system is still being defined, its introduction will not immediately replace the GSM-R but will work as an alternative to it.
It is important to underline that FRMCS allows communication only between the On-Board Subsystem and the RBC, while the GSM-R allows communication between the On-Board Subsystem and the RBC or RIU.
This means that the FRMCS cannot be used on ETCS L1 lines using the RIU.
The adoption of the FRMCS has introduced changes, especially in the definition of the procedure for managing the radio communication sessions.
The functional requirements for the FRMCS are listed in the document AT-7800 and included in the documental baseline.
Another innovation introduced in Baseline 4 R1 is the Automatic Train Operation.
ATO, the acronym of Automatic Train Operation, will make it possible to replace the presence of the driver by introducing (non-safety) functionalities relating to speed control, accurate stopping, door opening, and closing.
ETCS still ensures the security level in operations.
The ATO architecture can be schematized in the following mode.

As we can see, the ETCS On-Board Subsystem must interact with the ERTMS/ATO, a computer-based system that can substitute the driver for acting on the train’s traction/braking.
The ERTMS/ATO can be split in the following two blocks:
• ATO On-Board (ATO-OB): represents the subsystem and set of automated non-safety-related driver functions.
• ATO Trackside (ATO-TS): represents a set of functions that interfaces with the trackside systems which contain the operational data and infrastructure data required by the ATO-OB.
When the ATO is activated, a new operating mode called “Automatic Driving (AD)” has been defined. The transition in AD will be permitted only in Full Supervision mode .
For this new Operating Mode has also been defined the new icon to be displayed () and the relative position on the DMI (Rif. ERA_ERTMS_015560)

*icon
All the requirements relative to the ATO are indicated in the following documents:
• Subset 125 “System Requirements Specification”;
• Subset 126 “ATO-OB/ATO-TS FFIS – Application Layer”;
• Subset 148 “ATO-OB/ATO-TS FFIS – Transport and Security Layers”;
• Subset 130 “ATO-OB/ETCS-OB FFIS – Application Layer”;
• Subset 139 “ATO-OB/Rolling Stock FFIS – Application Layer”;
• 13E154 “ERTMS/ATO Glossary”.
In conclusion, this new Baseline has introduced numerous new features and technologies that will simplify and make possible the transition to a single railway infrastructure valid for the whole of Europe.
It is important to underline that the article indicates a general description of the main innovations introduced in Baseline 4 R1. In fact, these innovations/modifications have led to an important update of the requirements valid for the entire ERTMS/ETCS system split into the various reference documents of Baseline 4 R1.
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